"Rosaline," the film based on Rebecca Serle's omg-what-if?! retelling of "Romeo and Juliet" from the point of view of Romeo's jilted ladyfriend, has been in the development stage for, like, ever—and consequently surrounded by all kinds of rumors and speculation! (For instance: At one point, it was going around that Lily Collins would be starring as Rosaline; at another, unsourced reports suggested that the part of Romeo would be played by a badger wearing a codpiece and wig. Hollywood!)

But now, we have an officially sourced report from Deadline that the film has found its leading lady in none other than Allison Williams. FOR REAL.

Allison is best known for her work on "Girls," where she plays Marnie Michaels; this will be her first feature film, making her appearance in the starring role pretty dang impressive. "Rosaline" promises to be a twisty-interesting take on the classic Shakespearean tale of star-crossed lovers; the novel it's based on explores how Romeo and Juliet's tumultuous love affair and double suicide might have looked, in a modern-day setting, as seen through the eyes of Rosaline, the girl Romeo was supposed to be with before he suddenly surrendered his heart to her cousin. (In this version, "Juliet" is a psychotic, vindictive drama queen who ensnares the hapless Mr. Montague in her wild web of lies.) The project has been in development at 20th Century Fox for ages, but with the announcement of Allison's casting, it looks like things are moving forward.